213 research outputs found
The Large and Small Scale Structures of Dust in the Star-Forming Perseus Molecular Cloud
We present an analysis of ~3.5 square degrees of submillimetre continuum and
extinction data of the Perseus molecular cloud. We identify 58 clumps in the
submillimetre map and we identify 39 structures (`cores') and 11 associations
of structures (`super cores') in the extinction map. The cumulative mass
distributions of the submillimetre clumps and extinction cores have steep
slopes (alpha ~ 2 and 1.5 - 2 respectively), steeper than the Salpeter IMF
(alpha = 1.35), while the distribution of extinction super cores has a shallow
slope (alpha ~ 1). Most of the submillimetre clumps are well fit by stable
Bonnor-Ebert spheres with 10K < T < 19K and 5.5 < log_10(P_ext/k) < 6.0. The
clumps are found only in the highest column density regions (A_V > 5 - 7 mag),
although Bonnor-Ebert models suggest that we should have been able to detect
them at lower column densities if they exist. These observations provide a
stronger case for an extinction threshold than that found in analysis of less
sensitive observations of the Ophiuchus molecular cloud. The relationship
between submillimetre clumps and their parent extinction core has been
analyzed. The submillimetre clumps tend to lie offset from the larger
extinction peaks, suggesting the clumps formed via an external triggering
event, consistent with previous observations.Comment: 38 pages, 12 figures, accepted by Astrophysical Journal slight
changes to original due to a slight 3" error in the coordinates of the SCUBA
ma
The initial conditions of isolated star formation -- IX. Akari mapping of an externally heated pre-stellar core
We present observations of L1155 and L1148 in the Cepheus molecular cloud,
taken using the FIS instrument on the Akari satellite. We compare these data to
submillimetre data taken using the SCUBA camera on the JCMT, and far-infrared
data taken with the ISOPHOT camera on board the ISO satellite. All of the data
show a relation between the position of the peak of emission and the wavelength
for the core of L1155. We interpret this as a temperature gradient. We fit
modified blackbody curves to the spectral energy distributions at two positions
in the core and see that the central core in L1155 (L1155C) is approximately 2
degrees warmer at one edge than it is in the centre. We consider a number of
possible heating sources and conclude that the A6V star BD+67 1263 is the most
likely candidate. This star is at a distance of 0.7 pc from the front of L1155C
in the plane of the sky. We carry out radiative transfer modelling of the
L1155C core including the effects from the nearby star. We find that we can
generate a good fit to the observed data at all wavelengths, and demonstrate
that the different morphologies of the core at different wavelengths can be
explained by the observed 2 degree temperature gradient. The L1148 core
exhibits a similar morphology to that of L1155C, and the data are also
consistent with a temperature gradient across the core. In this case, the most
likely heating source is the star BD197053. Our findings illustrate very
clearly that the apparent observed morphology of a pre-stellar core can be
highly dependent on the wavelength of the observation, and that temperature
gradients must be taken into account before converting images into column
density distributions. This is important to note when interpreting Akari and
Spitzer data and will also be significant for Herschel data.Comment: 15 pages, 15 figures, accepted by MNRA
SCUBA and Spitzer observations of the Taurus molecular cloud - pulling the bull's tail
We present continuum data from the Submillimetre Common-User Bolometer Array
(SCUBA) on the James Clerk Maxwell Telescope (JCMT), and the Mid-Infrared
Photometer for Spitzer (MIPS) on the Spitzer Space Telescope, at submillimetre
and infrared wavelengths respectively. We study the Taurus molecular cloud 1
(TMC1), and in particular the region of the Taurus Molecular Ring (TMR). In the
continuum data we see no real evidence for a ring, but rather we see one side
of it only, appearing as a filament. We name the filament `the bull's tail'.
The filament is seen in emission at 850, 450 and 160um, and in absorption at
70um. We compare the data with archive data from the Infra-Red Astronomical
Satellite (IRAS) at 12, 25, 60, 100um, in which the filament is also seen in
absorption. We find that the emission from the filament consists of two
components: a narrow, cold (~8K), central core; and a broader, slightly warmer
(~12K), shoulder of emission. We use a radiative transfer code to model the
filament's appearance, either in emission or absorption, simultaneously at each
of the different wavelengths. Our best fit model uses a Plummer-like density
profile and a homogeneous interstellar dust grain population. Unlike previous
work on a similar, but different filament in Taurus, we require no grain
coagulation to explain our data.Comment: 10 pages, 9 Figures, Accepted by MNRA
The Initial Conditions of Clustered Star Formation. II. N2H+ Observations of the Ophiuchus B Core
We present a Nobeyama 45 m Radio Telescope map and Australia Telescope
Compact Array pointed observations of N2H+ 1-0 emission towards the clustered,
low mass star forming Oph B Core within the Ophiuchus molecular cloud. We
compare these data with previously published results of high resolution NH3
(1,1) and (2,2) observations in Oph B. We use 3D Clumpfind to identify emission
features in the single-dish N2H+ map, and find that the N2H+ `clumps' match
well similar features previously identified in NH3 (1,1) emission, but are
frequently offset to clumps identified at similar resolution in 850 micron
continuum emission. Wide line widths in the Oph B2 sub-Core indicate
non-thermal motions dominate the Core kinematics, and remain transonic at
densities n ~ 3 x 10^5 cm^-3 with large scatter and no trend with N(H2).
Non-thermal motions in Oph B1 and B3 are subsonic with little variation, but
also show no trend with H2 column density. Over all Oph B, non-thermal N2H+
line widths are substantially narrower than those traced by NH3, making it
unlikely NH3 and N2H+ trace the same material, but the v_LSR of both species
agree well. We find evidence for accretion in Oph B1 from the surrounding
ambient gas. The NH3/N2H+ abundance ratio is larger towards starless Oph B1
than towards protostellar Oph B2, similar to recent observational results in
other star-forming regions. Small-scale structure is found in the ATCA N2H+ 1-0
emission, where emission peaks are again offset from continuum emission. In
particular, the ~1 M_Sun B2-MM8 clump is associated with a N2H+ emission
minimum and surrounded by a broken ring-like N2H+ emission structure,
suggestive of N2H+ depletion. We find a strong general trend of decreasing N2H+
abundance with increasing N(H2) in Oph B which matches that found for NH3.Comment: 55 pages (manuscript), 15 figures, ApJ accepte
Networks and landscapes: a framework for setting goals and evaluating performance at the large landscape scale
The objective of large landscape conservation is to mitigate complex ecological problems through interventions at multiple and overlapping scales. Implementation requires coordination among a diverse network of individuals and organizations to integrate local‐scale conservation activities with broad‐scale goals. This requires an understanding of the governance options and how governance regimes achieve objectives or provide performance evaluation across both space and time. However, empirical assessments measuring network‐governance performance in large landscape conservation are limited. We describe a well‐established large landscape conservation network in North America, the Roundtable on the Crown of the Continent, to explore the application of a social–ecological performance evaluation framework. Systematic approaches to setting goals, tracking progress, and collecting data for feedback can help guide adaptation. Applying the established framework to our case study provides a means of evaluating the effectiveness of network governance in large landscape conservation
The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X
We have made an extensive 1.2mm continuum mosaicing study of the Cygnus X
molecular cloud complex using the MAMBO cameras at the IRAM 30 m telescope. We
then compared our mm maps with mid-IR images, and have made SiO(2-1) follow-up
observations of the best candidate progenitors of high-mass stars. Our complete
study of Cygnus X provides, for the first time, an unbiased census of massive
young stellar objects. We discover 129 massive dense cores, among which 42 are
probable precursors of high-mass stars. Our study qualifies 17 cores as good
candidates for hosting massive IR-quiet protostars, while up to 25 cores
potentially host high-luminosity IR protostars. We fail to discover the
high-mass analogs of pre-stellar dense cores in CygnusX, but find several
massive starless clumps that might be gravitationally bound. Since our sample
is derived from a single molecular complex and covers every embedded phase of
high-mass star formation, it gives the first statistical estimates of their
lifetime. In contrast to what is found for low-mass class 0 and class I phases,
the IR-quiet protostellar phase of high-mass stars may last as long as their
better-known high-luminosity IR phase. The statistical lifetimes of high-mass
protostars and pre-stellar cores (~ 3 x 10^4 yr and < 10^3 yr) in Cygnus X are
one and two order(s) of magnitude smaller, respectively, than what is found in
nearby, low-mass star-forming regions. We therefore propose that high-mass
pre-stellar and protostellar cores are in a highly dynamic state, as expected
in a molecular cloud where turbulent processes dominate.Comment: 32 pages, 62 figures to be published in Astronomy & Astrophysics
journa
Walk well:a randomised controlled trial of a walking intervention for adults with intellectual disabilities: study protocol
Background - Walking interventions have been shown to have a positive impact on physical activity (PA) levels, health and wellbeing for adult and older adult populations. There has been very little work carried out to explore the effectiveness of walking interventions for adults with intellectual disabilities. This paper will provide details of the Walk Well intervention, designed for adults with intellectual disabilities, and a randomised controlled trial (RCT) to test its effectiveness. Methods/design - This study will adopt a RCT design, with participants allocated to the walking intervention group or a waiting list control group. The intervention consists of three PA consultations (baseline, six weeks and 12 weeks) and an individualised 12 week walking programme. A range of measures will be completed by participants at baseline, post intervention (three months from baseline) and at follow up (three months post intervention and six months from baseline). All outcome measures will be collected by a researcher who will be blinded to the study groups. The primary outcome will be steps walked per day, measured using accelerometers. Secondary outcome measures will include time spent in PA per day (across various intensity levels), time spent in sedentary behaviour per day, quality of life, self-efficacy and anthropometric measures to monitor weight change. Discussion - Since there are currently no published RCTs of walking interventions for adults with intellectual disabilities, this RCT will examine if a walking intervention can successfully increase PA, health and wellbeing of adults with intellectual disabilities
MAMBO Mapping of Spitzer c2d Small Clouds and Cores
AIMS: To study the structure of nearby (< 500 pc) dense starless and
star-forming cores with the particular goal to identify and understand
evolutionary trends in core properties, and to explore the nature of Very Low
Luminosity Objects (< 0.1 L_sun; VeLLOs). METHODS: Using the MAMBO bolometer
array, we create maps unusually sensitive to faint (few mJy per beam) extended
(approx. 5 arcmin) thermal dust continuum emission at 1.2 mm wavelength.
Complementary information on embedded stars is obtained from Spitzer, IRAS, and
2MASS. RESULTS: Our maps are very rich in structure, and we characterize
extended emission features (``subcores'') and compact intensity peaks in our
data separately to pay attention to this complexity. We derive, e.g., sizes,
masses, and aspect ratios for the subcores, as well as column densities and
related properties for the peaks. Combination with archival infrared data then
enables the derivation of bolometric luminosities and temperatures, as well as
envelope masses, for the young embedded stars. CONCLUSIONS: (abridged) Starless
and star-forming cores occupy the same parameter space in many core properties;
a picture of dense core evolution in which any dense core begins to actively
form stars once it exceeds some fixed limit in, e.g., mass, density, or both,
is inconsistent with our data. Comparison of various evolutionary indicators
for young stellar objects in our sample (e.g., bolometric temperatures) reveals
inconsistencies between some of them, possibly suggesting a revision of some of
these indicators.Comment: Accepted to A&A. In total 46 pages, with 20 pages of tables, figures,
and appendices. High-resolution version of this article at
https://www.xythosondemand.com/home/harvard_iic/Users/jkauffma/Public/mambo_spitzer.pd
The prestellar and protostellar population of R Coronae Australis
We present 450 and 850 um maps of R Coronae Australis. We compare the maps to
previous surveys of the region, and shed new light on the previously unknown
nature of the protostellar sources at the centre of the cloud. We clarify the
nature of two millimetre sources previously discovered in lower resolution
data. We identify one new Class 0 protostar that we label SMM 1B, and we
measure the envelope masses of a number of more evolved protostars. We identify
two new prestellar cores that we call SMM 1A and SMM 6.Comment: 8 page
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